Abstract

Magnetic skyrmion, topologically stable spin swirls with a particle-like character, has been intensively investigated as a candidate for high-density information storage. In this study, we addressed two emerging trends in skyrmion research that have gained prominence over the past five years.

The first focus is the formation mechanism of skyrmion lattice states in centrosymmetric rare-earth intermetallics [1]. In these systems, the Dzyaloshinskii-Moriya interaction, which has traditionally explained many instances of skyrmion formation, is not allowed, necessitating an alternative mechanism. While theoretical investigations are abundant, experimental validation is still limited, leaving this topic an open and controversial area of investigation. We combined various physical property measurements, not limited to the magnetic probes commonly used in skyrmion research. Our results show the significant role itinerant electrons play in skyrmion formation [2].

The second topic concerns “skyrmion strings.” In three-dimensional systems, skyrmions stack along the third direction, forming a string-like object. These skyrmion strings have recently been experimentally observed in bulk crystals. The characteristics beyond the particle-like framework are expected to expand skyrmion application possibilities. We particularly focus on phonon properties. Employing ultrasound measurements, we discovered non-reciprocal phonon transport likely related to magnon excitations in skyrmion strings [3,4].

[1] Y. Tokura and N. Kanazawa, Chem. Rev. 121, 2857 (2021)
[2] N. Matsuyama et al., Phys. Rev. B 107, 104421 (2023)
[3] T. Nomura et al., Phys Rev. Lett. 122, 145901 (2019)
[4] M. Garst et al., J. Phys. D; Appl. Phys. 50, 293002 (2017)